Work operations are often performed on multiple layers of sheet-type work material, for example, in the mass production of garments, pattern pieces are usually cut from multiple layers of fabric spread one-on-top-of-the-other on a support surface. To facilitate clean accurate cuts, the layers of work material, often referred to as a lay, must be adequately held in place on the support surface during the performance of a cutting operation. Failure to do so can result in movement of the fabric layers relative to one another, detrimentally affecting the performance of the cutting operation.
Generally, pattern pieces are cut from the lay using what is referred to as a cutter table that usually includes a permeable, often conveyorized, cutting surface and a moveable cutter head that traverses the support surface, cutting pattern pieces from the layers of material in response to commands issued from a controller. To eliminate any undesired movement of the layers of work material during the performance of a work operation, vacuum is sometimes used in an effort to draw the work material against the support surface. In prior art cutter tables this was usually accomplished via a single centrally located vacuum manifold positioned under the permeable support surface and defining one or more inlets through which vacuum is drawn.
A difficulty sometimes encountered when a single centrally located vacuum manifold is employed, is that the portions of the work material located remotely from the manifold tend to be inadequately retained by the vacuum. This inadequate retention can result in movement of the work material during the performance of a work operation, and the generation of inaccurately cut pattern pieces. This problem is further exacerbated as the cutter tables increase in width.
In the past, efforts to address the above-described problems have failed. In one proposed solution, the inlets in the centrally located manifold were enlarged to increase the vacuum drawn there through. However, the enlarged inlets weakened the vacuum manifold to such an extent that it deformed during operation.
Another proposed solution was to increase the intensity of the vacuum drawn through the inlets. However, in cutting tables where the support surface was conveyorized and movable relative to the frame, the increased vacuum concentration caused the support surface to be drawn against the vacuum manifold, thereby hindering the movement of the support surface relative to the manifold.
Based on the foregoing, it is the general object of the present invention to provide an apparatus and method for retaining multiple layers of sheet material against a support surface that overcomes the drawbacks of prior art methods and apparatus for retaining sheet material.
It is a more specific object of the present invention to provide a method and apparatus which applies vacuum to the layers of sheet material adjacent to the location of the performance of a work operation.